Bagasse burning furnace



Feb. 19, 1935. c; G. BRowN BAGASSE BURNING FUHNACE Filed June 50. 1930 DDU .ll-lil lDU DDD D DD sllii nu ou fe .E- I,...

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wuentoz CARL G. BROWN.

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Patented Feb. 19, 1.935

UNITED STATES BAGAssE Vi' ...'rr.N'r OFFICE BURNING FURNACE The invention relates in general to a furnace particularly designed for the burning of bagasse, sawdust, tan bark, rice hulls and similar types of fuel having a high percentage of water content, and the invention specifically relates to a masonry setting for water tube and other forms of boilers of conventional design, and which setting is formed of refractory material and designed to form a front fireplace for burning the bagasse and to form a rear and improved design of combustion chambers and passageways for mixing and conducting the resulting hot gases to the boiler for heating the same.

The primary object of the invention is to provide a simplifiedand improved form of furnace of this type which will have a higher thermal efficiency than similar forms of steam generating plants now known, and which will minimize the time necessary to cleanthe boilers from soot and other deposits resulting from the burning gases obtained from the firing of wet fuel such asbagasse.

It has been found in burningbagasse and other wet forms of fuel that large quantities of solid,

fine particles of matter are suspended in the gases 30 tubes and other heat abstracting parts of the boiler with resulting necessity of an almost daily shutting down of the plant in order to clean the boilers.

The present disclosure features a -furnace of the Dutch oven type with-a masonry construction which provides a fireplace, or primary combustion chamber extending forwardly .of the boiler construction, and into which fireplace the bagasse or other wet fuel is fed conventionally, and a secondary combustion passageway primarily designed to effect a vcomplete combustion of the fired gases. To attain this effect the parts are designed to receive the relatively cold burning gases` which are discharged at high velocity from the 1.a lined' by refractory. material and thus cause a with resulting high heat losses and reduced ther- `the intent to utilize for the purpose of generating compartments.

primary combustion chamber, to slow downtheir complete combustion before the hot burning gases are discharged into the boiler or other heat abstracting parts of the furnace.

This requirement for a long passageway to insure complete combustion of the burning gases 5 would ordinarily necessitate a furnace of impractical length in situations Where economy in space is vitally necessary and any long furnace structure would result in exposure of heated parts l0 mal eiciency in the plant.

Accordingly another object of the invention is to provide a furnace of the type outlined which will be compact, of relatively small allover dimensions, particularly in floor space covered; which will be characterized by minimum length; which will feature a disposition of partsto minimize heat losses, especially extraneous heat losses in the high temperatured parts of the burning gases; which will direct its hottest gases to the hotter end of the boiler and which will utilize any heat transmitted through the crown wall forming the top of the long combustion passageway to supply added heat to the colder end of the boiler; and in general the design of the gas passages -is with steam the maximum of thermal units present in the wet fue'l.

` Among Ithe other objects of the invention are to provide a boilerl construction which will provide ready access to the fireplace or primary combustion chamber to facilitate the feeding of fuel thereto; which provides ready access to the relatively cold end of the boiler parts for inspection and repair; and which provides for the ready removal from the combustion passageway of incombustible materials which have been whirled out of the gases as they pass along the secondary combustion chamber and boiler containing Various other objects and advantages of th invention will be in part4 obvious from an inspec-. tion of the accompanying drawing, and in part will be more fully set forth in the following par. ticular description of one form of device embody- 4 ing my invention, and the invention also consists in certain new and novel features of construction and combination of parts hereinafter set forth and claimed.

In the accompanying drawing;

Fig. 1 is a vertical sectional view taken longitudinally of a furnace andk taken on the line 1-1 of Fig.- 2, illustrating a preferred embodiment of the invention in connection with a duplex fireplace and combustion chamber but it 55 is understood that the fireplace and combustion chamber may be of the single type or any number of such gas forming parts may lbe utilized, especially in cases where a relatively wide type of boiler is utilized.

Fig. 2 is a vertical sectional view taken on the line 2-2 of Fig. 1, looking in the direction indicated by the arrow, and` Fig. 3 is a detailed plan view showing Aa portion of the gas passageway looking down from the plane indicated by the line 3--3 of Fig. 1.

In the drawing there is disclosed a masonry construction 10 mounted on a suitable foundation 1l and providing a setting for a boiler 12. The boiler illustrated is of a conventional form including an inclined bank of water tubes 13, headers 14 and'l, connecting tubes 16, and transverse drum 1'?, the latter being supplied with exposed gauges and indicators 13, and in general it is understood that the boiler is of a conventional form and this form has been illustrated simply to show adaptability of the inventive features toa known form of boiler construction. It is obviously within the scope of the disclosure to utilize a boiler construction in which the drum 17 extends parallel to the bank 13.

` Referring primarily to the refractory' lined masonry construction 1G, it will be noted that it consists primarily of a major portion 19 inwhich is contained a boiler and an extension 2G projecting forwardly from the lower part of the major portion 19 to form a Dutch oven construction. The forward extension provides a primary combustion chamber 21 which constitutes the repit in which the fuel is burned. The chamber 21 is deiined on its forward side by an upstanding front wall 22 and at its rearside by an inner wall 23. The top of the combustion chamber 21 is dened by the forward portion of crown wall 24 which extends from the front wall 22 into the major portion 19 ,as hereinafter described.

I'he chamber 21 is provided with a fuel inlet `25, in the instant case equipped with a bagasse a primary bridge wall 28 and there above the crown walllis provided with a depending arch 29 hereinafter referred to as a mixing arch coacting with the wall 28 to formv a short constricted passage 30 constituting an outlet for the burning gases discharged from the combustion chamber 21. It is the intent of this disclosure to cause the relatively cold burning gases to be discharged from the primary combustion chamber 21 through the mixing arch 29 and into a secondary combustion chamber at high speed, and accordingly the passageway 30 is peculiarly designed to accomplish this purpose.

I'he major portion 19 of the masonry construction forms an 'L-shaped secondary combustion passageway 31. This passageway includes a horizontally extending gas-receiving part 32, one end ofv which is -open to receive gases discharged through-the passage 30. The passageway v31 .also

includes a vertically extending gas discharge part 33, and this passageway is so designed that it gradually increases in cross sectional area from its gas receiving` end at the passage 30 to its discharging end formed by the vertically extending part 33 which is of uniform cross sectional area adjacent its upper end. .The top of the horizontally extending part 32 is outlined by the inner horizontally extending part of crownwall 2d and terminates in spaced relation to a rear wall 34, which forms the rear end of the construction arid denes the rear sides of both the passageway parts 32 and 33..' The opposite or forward side of this part 33 is dened by a wall 35 which extends upwardly from the inner end ci the crown wall 24. A floor 36 extends from the bridge wall 28 to the rear wall 34 and defines the bottom of the horizontal passageway part 32.

It is a feature of this disclosure that this floor 36 is designed to cause the gases to whirl upwardly at the inner end of the part 32 and about transverse axes as indicated by the curved arrow a in Fig. 1, and for this purpose the iioor 33 is shaped to have somewhat of a parabolic form, with its long downwardly inclined portion 3? extending from the bridge wall 28 to a lowermost point 38, defining the bottom of the vertically extending part 33, and havingv an upwardly extending portion 39 rounding into the inner side of wall 24 at a sharp angle indicated at 39.

From this construction it is notlid that the gases discharged from, the part of the construction containing the primary combustion chamber pass along a somewhat U-Shaped passageway, the lower leg of which is formed by the horizontally extending part 32, the crotch by the vertical part 33 and the upper leg by the boiler containing chamber 42, thus conning the high temperatured burning gasesto the major construction 19.

The setting construction is provided at the lowermost portion 33 of the floor 36 with a normally closed cleanout door 40, and similarly the construction is provided at the top of the crown wall 24 with a cleanout door 41. From this construction it will be seen that means are provided at the low levem of the secondary combustion passageway 31 and at the low level of the boiler containing compartment 42 above the crown wall 24 to facilitate cleaning ofthe furnace of any soot or other material trapped at these points of the construction. l

Under someA conditions the providing of the passageway 31 as thus described with its gradual increase in volumetric capacity from its gas receiving towards its discharging end and the long upwardly sweeping curve'at the elbow of the combustion zone provides suflicient turbulency to effect a thorough mixing of the gases to ob` tain the desired elfects. I t is further suggested that. meansbe also provided to give the gasesa whirl abouttheir longitudinal axis of travel, and for this purpose one or both of the arches outlining the passagel30` or the exposed surfaces at top or bottom of vthe passageway part 32 are ried.

Referring tothe showing in Fig. 3, it will be noted that the vtop of the bridge wall is provided with a plurality of grooves 43 inclined at a slight 'angle to the path of movement of the `gases across this bridge wall and/'inclined at an/angle 1 to the length of the arch. f" Itis within the scope of this disclosure to provide the upper arch 29 with similar angularly disposed grooves. By such means the gases are given a whirl, in this case in a clockwise direction, as indicated bythe arrow b, as they pass into the long combustion passageway 31. i

Similarly the iioor 36 and particularly the part adjacent thepassageway 30 is scored, grooved an opportunity 'for completing the combustion of 'tend to whirl back upon themselves, as indicated or rifled spirally, as indicated at 44 in Fig. 3, and these grooves are disposed to create a whirl in the gases in the event that grooves 43 are omitted at the passage 30 or to assist in maintaining the whirl in the event that the gases are already rotating by virtue of passing through the passage 30. While floor 36 has been shown lat and horizontal when considered transversely, it is within the scope of the disclosure to curve it so that it will be channel shape in cross section and it may be formed one side higher than the other or otherwise modied following conventional practices in creating turbulency in gases vto effect the maximum agitation in the gas flow.

Referring to the boiler construction it will be noted that it is confined substantially within the upwardly projected outlines of the major gas passageway containing part 19, thus leaving the top of the extension 20 exposed for easy access. The elevated rear header 14 rests upon the top of steel columns (not shown) contained in the rear wall 34 and the lower, front header 15 rests upon I-beam supports'45 forming part of the crown wall construction at the front end of the boiler. The` boiler construction also includes a conventional form of roof structure 46 provided with a stack opening 47 and to one side of which depends a hanging bridge wall 48; and the boiler construction also includes enclosing metallic shell parts, including doors 49 and 50, following conventional practices in this respect.

A rst baille 51 is supported from the wall 35 and a second baille 52 depends from the hanging bridge wall 48. The disposition ofthe boiler parts with these baffles forms aflrst pass 53', constituting an upward extension and prolongation l of the gas discharging part 33 between the header '14 and the first baiile 5l. 'Bales 51 and 52 form a second pass 54, and the baille 52 and header 15- and front end of the boiler forms a third pass 55 which discharges its gases upwardly past the inner side of drum 17 through opening 47 into stack 56. `Means are provided for supplying combustion supporting air to the burning gases and for this purpose external air is supplied to the combustion chamber 21 through an air intake 57- extending through the'crown wall 24 and similarly an air intake 58 extends through the rear wall 34 to supply air to the L-shaped secondary passageway 31.

In operation it will be understood that the bagasse or other fuel is introduced through the fuel inlet 25 and is permittedto burn on grate 26. The burning gases with the solid particles entrained therein are discharged across the mixing arch 29 and through the constricted passage 30 at high velocity. )As the gases pass across the bridge wall they will ordinarily be given some whirling'action even in the absence of the angularly disposedgrooves or rifling, but the presence of any such grooves or baflles will more positively insure a whirl to the gases at their point of maximum velocity and about a longitudinal axis, as indicated by the arrow b.

As the gases move into the secondary chamber 31 they gradually lose their initial high velocity due to the gradual increase in cross sectional area of this passageway, thus slowing down the rate of 'movement and providing for a delay in the lapsed time before the gases reach the boiler. This slowing down of their forward velocity while increasingthe length of gas travel spirallyaflords all the gas. As the gases sweep down the inclined side of the parabolic form of bottom they will by the long curved arrow a, and thus will have the effect of still more thoroughly mixing the unburned combustible material present with the combustion supporting air, and thus eiiect a more complete combustion than would be the case if the peculiar form of gas turning bottom was not present. This whirling a-nd turbulent action of the gases at the bottom of the vertical part 33 of the combustion chamber has the effect of precipitating any unburned solid material at the lowermo'st point of the combustion chamber and in position where such deposited material may be readily Withdrawn from the furnace through opening 40 in cleaning the same. The parts will be proportioned and the oor so designed that a considerable amount of deposited material may accumulate at the low point of the passageway without seriously affecting the operation of the furnace, and'in this way itis possible to run the furnace for a relatively long period of time before it becomes necessary to clean the same.

As the burning gases pass across the mixing arch 29, and alongthe crown wall 24, they have the effect of heating the arch crown wall to in candescence which in turn has the eiect of radiating its heat back to the gases thus maintaining lthem at a high temperature and insuring the combustion of those carbon radicals in the gases which oxidize only at high temperatures. As the crown wall is enclosed it will have a tendency to become intensely heated and the organization i and arrangement of parts disclosed are particularly designed to minimize outside heat losses by radiation through this wall. The arch shaped throat or passageway 30 is particularly designed to cause the gases, to mix as they pass under the mixing arch 29 but it is understood that it may be of any conventional design. It will be seen that the gases are subjected while in the long secondary combustion passageway not only to a turbulent action due to the'conguration of the same but are also subjected to heat radiated from the walls outlining `the passageway and particularly to the upper wall forming the crown wall 24.

As the gases pass upwardly through the part 33 of the combustion chamber, the combustion act will be completed and the gases which-are at this time at their maximum temperature will be directed on to the bank of tubes at their hotter end, which is disposed across thetop of the part 33 and across the first pass 53. The gases, robbed of a portion of their heat at the upper ends of the tubes, will be deiiected downwardly from roof 46 into the second pass 54 and will then pass along a U-shaped passage, and-be deflected from the top of crown wall 24 upwardly into the third pass 55. As the gases are passing along the second and third passes they are subjected to the heating effect of heat transmitted through the portion of the crown wall 24 beneath the same, and in this way heat which would otherwise be lost, if the crown wall were exposed, is retained and utilized to assist the gases in heating the colder end of the boiler. 'I'he gases before being passed from the furnace are still further deprived of their heat content by contact with the water rum 17 so that when finally discharged through the stack 56 the maximum amount of their contained heat has been abstracted and utilized to been possible to attain the advantages heretofore recited in the statements of objects of the invention. It is particularly noted that the Dutch oven construction permits ready access to the primary combustion chamber, and this relatively cold portion of the construction is removed from the hot portion of the furnace whichgoes to make up the part in which the burning gases reach their highest temperature. The boiler is disposed in position over this hot part of the construction and is thus disposed in position to receive heat from the burning gases as well as from the intensely heated portion of this part of the fuel setting. The` high temperature containing parts of the structure are designed so as to minimize features which would tend to permit heat losses. While the construction features a long gas burningpassageway the design is such that space, and particularly floor space, is economized, and in general there is provided a highly efficient, compact form of furnace particularly designed to burn bagasse and similar l wet forms of fuel.

I claim:

1. In a furnace of the Dutch oven type, the combination of a setting construction comprising a rear major portion and an extension extend- `ing forwardly and integrally from the lower part of the major portion, said major portion including in superposed order a secondary, L-shaped combustion passageway and a boiler containing chamber, bailles in said chamber dividing the same from rear to front into first, second and third passes, said passageway including a horizontally extendingv gas receiving part and a vertically extending gas discharging part, said passageway increasing in crosssectional area from its receiving end towards its discharging part, said discharging part opening upwardly into the first pass, said major portion provided with a stack opening communicating with the forward or third pass to receive the products of combustion discharged from the furnace, and said forward extension offset forwardly from the boiler containing chamber and having its upper side exposed, said extension containing a primary combustion chamber and a constricted opening placing the primary chamber in communication with the forward gas receiving end of the secondary combustion passageway, a crown wall defining the top of said primary combustion chamber and the top of said secondary passageway in advancev of the'discharge passageway, boiler supporting means carried by said crown wall between the primary combustion chamber and said passage- Way and said forward extension provided in thesaid construction including a crown wall out-- lining the top of said horizontally extending part and a boiler positioned above and substantially oifset horizontally from said chamber thereby to leavexposed both the top of the construction containing said chamber and the front end ofthe boiler, and said boiler having one end extending across the vertically extending part of the combustion passageway and there subjected to the direct heating action of the burning gases discharged from said passageway and having its other end overlapping said crown wall to receive heat transmitted upwardly therethrough from the horizontal part of said passageway.

3. In a furnace of the Dutch oven'type, the combination of a masonry boiler setting construction including a front wall, a rear wall, a crown wall extending horizontally from the front wall and terminating at its inner end in spaced relation to the rear wall, a wall extending upwardly from said inner end and coacting with the rear wall to form a vertically extending part of a secondary combustion passageway, an inner wall in spaced relation to the front wall and forming therebetween a primary combustion chamber outlined at its .top by the front portion of the crown wall, a floor extending from the innerwall and curving therefrom downwardly in a jlong sweeping line and then sharply upwardly into the rear wall, the

i space between said oor andthe rearfportion of the crown wall forming a horizontally extending part of the combustion passageway opening upwardly into thevertically extending part, and a boiler-having yone end offset from the primary combustion chamber, positioned in advance of said upwardly curved portion of said oor, overlapping the vertically extending part o1' the pasthe rear portion of the crown wall.

4. In a furnace of the type described, the combination of a masonry boiler setting including a structure providing an integral front wall, a. bridge wall coacting therewith to form a primary combustion chambena rear wall, a :door extending from the bridge wall to the rear wail, a crown wall extending horizontally forming the top oi the combustion chamber, and extending therefrom in spaced relation above the door to form a secondary combustion wall land projecting slightly into the combustion chamber, the rear end of the arch being spaced, slightly above the top cik the bridge wall to form a short constricted passage between said chamber and passageway, said passageway increasing in cross sectional area from the end adjacent the combustion chr towards itsother end-'and said iloor' being substantially of a parabolic form considered from a line slightly below the top of the bridge wall towards the rear wall and said setting provided with means for supporting a boiler in spaced relation above the crown wall. p

5. In a furnace of the type described, the combination of means forming 'a primary combustion chamber provided with a fuel inlet and with a gas outlet constricted to cause the burning gases discharged from the primary combustion chamber to move at high velocity, means providing an L-shaped secondary combustion passageway having a horizontally extending part with a gas receiving end open in vertically spaced relation to both its upper and lowerportious to receive gas discharged through said gas outlet approximately mid-height of the passageway, with a vertically extending gas discharging part, said horizontally extendingpart rapidly increasing in cross sectional area. from its receiving towardsl its discharging end and having the portion of its lbottom below the vertically extending part of the passageway curved at an angle to both the horizontal and vertical whereby gases passing along the hori- Y zontal part are caused to be whirled into the sageway and having the other end overlapping vertically extending part of the passageway, and a. boiler positioned above the secondary combustion passageway and having a part extending across said vertically extending part and disposed in the path of the gases whirled from said inclined portion of the bottom.

6. In a furnace of the'type described, the combination of means forming a primary combustion chamber and an L-shaped secondary gas combustion passageway to receive burning gases from the chamber, said passageway having a horizontally extending gas receiving part and a vertically extending gas discharging part, a crown wall outlining the top of the horizontal part, a wall projecting upwardly from said crown wall and outlining one side of the vertical part, a rear wall outlining the opposite sidel of the vertical part, a floor outlining the bottom of the horizontal part and c urving upwardly into the rear wall with a substantially parabolic curve having its lowermost portion at the bottom of the vertical part, a boiler having one end supported on the rear wall above said upwardly curved part of said Iloor, having its other vend supported on the means forming the primary combustin chamber and a baille for said boiler supported by said wall projecting upwardly from the crown wall.

7. In a furnace of the type described, the combination of means providing a primary combustion chamber, a long horizontally extending secondary combustion passageway and a constricted passage placing the chamber and passageway in communication, said passage outlined on one side by a long structural member, having grooves therein extending at an angle to its length and at an angle to the direction of iow of the gases through said passage and acting on the gases passing through the passage to cause them to whirl about their path of longitudinal inovement, as they move from the combustion chamber into the long secondary passageway.

8. In a furnace of the type described, the combination of means providing a primary combustion chamber, a long horizontally extending secondary combustion passageway and a constricted passage placing the chamber and passageway in communication, said passage outlined on one side by a long structural member having grooves therein extending at an angle to its length and at an angle to the direction of ow of the gases through said passage and acting on the gases passing through the passage to cause them to whirl about their path of longitudinal movement as they move into the long secondary passageway, and said passageway outlined on one side by a grooved faced construction in which the grooves are of spiral form and disposed to give the gases a whirl about their path of movement as they pass along the secondary passageway.

9. In afurnace of the type disclosed, the combination of means providing a primary combustion chamber, a secondary. combustion passageway and. a passage placing the chamber and passageway in communication, and said passageway outlined on one side by a grooved xed construction in which the grooves are of spiral form and'disposed to give the gases a whirl about their path f movementas they pass along' the secondary passageway.

10. In afurnace of the type disclosed, the combination of means providing a primary combustion chamber, a secondary combustion passageway and a passage placing the chamber and passageway in communication, and said passageway outlined on one side by a grooved faced construction in which the grooves are of spiral form and disposed to give the gases a whirl about their path of movement as they pass along the secondary passageway, and said grooved face construction being curved at one end to cause the whirling gases whirling about such path of movement to be given an additional whirl about an axis'transverse of said path of movement.

11. In a furnace of the Dutch oven type, the combination of a masonry construction providing a primary combustion chamber containing part and a boiler containing part horizontally offset therefrom, said latter part provided within its outlines with a tortuous gas passageway substantially U-shaped considered as lying on its side and comprising a lower horizontally extending gas combustion passageway open at one end to receive said boiler containing chamber, spaced'above thehorizontally extending passageway to form a gas chamber therebetween, overlapping the vertically extending part of the passageway and exposed to the heating action ofthe gases passing therethrough and said boiler including ballles forming the boiler containing chamber into a tortuous passageway leading from the upwardly extending continuation to the stack opening.

12. In a device of the class described, the combination of a masonry construction forming a primary combustion chamber, a horizontally oiset secondary combustion passageway, a connecting passage therebetween outlined at its top by a mixing arch and at its bottom by a bridge wall the opposing faces of both the bridge wall and arch being rifled, both extending one above the other in parallel relation transversely of the length of the secondary combustion passageway, both the bridge and arch having relatively small width in the direction of the length of the passageway and both capable of becoming incandescent, and means forming a boiler containing chamber overlapping said passageway, positioned above the arch and open to the passageway.

l 13. In a device of the class described, the combination of a masonry construction including a crown wall provided midlength with a depend-l ing mixing arch, outlining the top of a constricted throat and a -bridge wall outlining the bottom of said throat, said structure forming on one side of the throat a primary combustion chamber and on the other side a secondary cornbustion passageway, the parts outlining said throat extending in parallel arched relation and adapted to .be heated to incandescence by the burning gases passing across the same, and which gases become mixed as they pass across the mixing arch the opposing faces of both the bridge wall and arch beingriiled, and a boiler containing chamber open to the end of said passageway remote from the constricted throat.

14. In a furnace of the Dutch oven type, the combination of a masonry construction compris- 'ing a front wall, a' rear wall and an inner wall therebetweemthe front and inner wall defining the front and rear sides of a primary combustion chamber, a secondary combustion chamber between the inner and rear walls having a long horizontally extending receiving portion and an upwardly extending discharge portion, a bottom to thesecondary chamber forming a substantially parabolic curve merging sharply upwardly into the rear wall, a crown wall having its forward portion outlining the top of the primary chamber and its rear portion outlining the top of the horizontal portion of the secondary chamber, a baille wall extending upwardly from the rear end of the crown wall andcoacting with the rear wall to define the front and rear sides of the discharge portionof the secondary chamber, an arch depending from lthe crown wall and coacting with vthe top of the inner wall to form a constricted passageway betweenthe primary and secondary chambers, a boiler supported at its rear end on the rear wall and at its front end on that portiony of the crown wall which is above vthe arch andv overlapping the baiile wall, and means providing ing a front wall, a rear wall and an inner wall therebetween, the front and inner Wall defining.

the front and rear sides of a primary combustion chamber, a secondary combustion chamber between the inner and rear walls having a long horizontally extending receiving portion and an upwardly extending discharge portion, a bottom to the secondary chamber forming a substantially parabolic curve merging sharplyupwardlyinto the rear wall, a crown wall vhaving its forward portion outlining the top of the primary chamber and its'rear portion outlining the top of the horizontal portion of the secondary chamber, a baiile wall extending upwardly from the rear end of Vthe crown wall and coacting with the rear wall to define the front and rear sides of the discharge portion ofthe secondary chamber, -a first baille carried by and extending above the baiiie wall, a. roof, a hanging bridge wall depending from the roof, an arch depending from the crownwall and coacting with the top of-the inner wall to form a constricted passageway between the primary and secondary chambers, that .portion of thecrown wall which is above the arch and overlapping the baille wall providing a boiler support, and means providing access to the primary chamber through y the crown wall.

16. In a device of th'e class described, the combination of means including a front wal1,.an inner wall and a crown wall forming a primary combustion chamber, means including a horizontal extension of the crown wall and a floor extending from the irmer wall forming a secondary horizontally extending passageway, a bridge wall projecting upwardly from the inner wall and above the floor, an arch abovethe bridge wall way and said sharply curving end' of the para- A bolic floor merging upwardly into the inner side of the rear wall.

17. In a device of the class described, a structual part forming agas conduit including a primary combustion chamber, a secondary combustion chamber, and a constrictive passage connecting the two chambers, said secondary combustion chamber gradually increasing in cross-sectional area from the constricted passage towards its discharge end, and a. side of both the passage and the secondary chamber provided with grooves inclined at an angle to the direction of movement of the gases through the passage and secondary chamber to cause the gases to whirl `as they pass through the passage and secondary chamber.

18. In a device of thev class described, a construction forming a gas conduit including a primary combustion chamber, a secondary combustion chamber and a connecting passage, a part of said construction beyond lthe primary combustion chamber provided with a spiral riing for causing the gases .to assume a whirl as they pass along said rifling. i'

19. In a furnace of the type described, the combination of a construction providing a combustion chamber, and a gas conduit leading therefrom,

the part of the construction outlining the gas conduit provided with riing means for causing the gases to whirl as they move along said conduit. 20. In a furnace of the Dutch oven type,` the combination of a structural part providing a combustion chamber having a fuel inlet in the top wall thereofand providing an L-shaped gas conduit with a horizontally extending gas intake end opening through a constricted vpassage from the combustion chamber and with a gas discharge Aend remote from the combustion chamber extending vertically to provide a vertically extending passageway projecting fora substantial distance above-the level of the top of the combustion chamber, the vertical length of the vertically extending passageway being greater than the length of the horizontally extending gas intake end measured from its gas intake end to said vertically extending passageway and a boiler'having one end overlapping the upper part of said Vertically extending end of the gas conduit, and

.said structural part providing a screen for preventing exposure of the boiler directly to the burning fuel in the combustion chamber.

21. In a furnace of the Dutch oven type, the combination of a structural part including a crown wall, an inner wall and'a front wall coacting to form a primary 'combustion chamber, said structural part also including a floor, a rear vvall,` a roof, an extension of the crown wall having an upstanding wall at its inner end parallel to and spaced forwardly from the rear wall, forming a gas conduit substantially L-shaped in vertical section with a.' horizontal part constituting a gas receiving part, a constricted passage forming com munication between the combustion chamber and the intake end of said horizontal part and a vertical gas discharging part, the longitudinal distance of said vertical part 'measured between the floor and roof being greater ,than the longitudinal distance of v said horizontal part measured between the irmerwall and the rear walland a boiler having an end extending into the upper portion of the vertical part above the wall at the inner end of the crown wall.

' 22. In a furnace of the Dutch oven type, the combination of structural means forming a gas conduit including a rear wall and another wall spaced therefrom, extending parallel thereto and LQQLSWS coasting to term a vertically extending gas discharge part, a crown wall and a door vertically spaced and coacting to form a gas receiving part oi the conduit, the floor being of parabolic form and curving from the gas receiving end downwardly into a curve of relatively long radius and curving at the portion denning the bottom of the vertical part into the rear wall with a curve of relatively short radius, means providing a combustion chamber horizontally offset from the structure, means forming the gas conduit and a constricted passagebetween the combustion 'chamber and the receiving end of said gas conduit.

23.In a furnace of the Dutch oven type, the combination of means forming a primary combustion chamber of compact form, means forming a boiler containing chamber of relatively large dimensions positioned above the level of the top of the combustion chamber, means forming a long i.-shaped passageway having a horizontal part opening at one end through a constricted passage into the combustion chamber and having averticai part opening at its upper end through a wide unrestricted outlet to the boiler containing chamber, the balance oi the boilercontaining chamber overlapping the intake end of the,

horizontal part of the L-shaped passageway, the horizontal part increasing in cross sectional area from the intake end at the constricted passage towards the bottom of the vertical part whereby the gases discharged from the combustion chamber through the constricted passage are caused to expand while moving horizontally and to ow freely upwardly before they are discharged into the boiler containing chamber.

24; In a Dutch oven furnace, the combination of a structural part'including a front wall, an

inner wall and a crowntwail coacting toprovidea compact primary combustion chamber provided witha fuel inlet and an air inlet in the crown wall, a boiler containing chamber, an L- shaped secondary passageway, an arch depending from the crown wall and a bridge wall projecting upwardly from the inner wall and coacting to form a constricted passage between the primary combustion chamber and the .secondary passageway, said passage providing an. outlet for the burning gas in the combustion chamber and at the same time restraining the freedom oi iiow of the gas thereby to provide heat to dry the fuel in the combustion chamber, said secondary passageway including. a horizontally extending part receiving burning gas from the passage and a vertically extending part opening at its upper end into the boiler containing chamber, and natural draft means for supplying external air to the burning gas in the horizontally extending part or the secondary passageway.

25. In a Dutch oven furnace, the combination of a structural part including a iront wall, an inner wall and a crown wail coacting to provide a compact primary combustion chamber provided with a fuel inlet and an air inlet in the crown wall, a boiler containing chamber, an L-shaped secondary passageway, an arch depending from the crown wallv and a bridge wall projecting upwardly from the inner wall and coacting to form a constricted passage between the primary combustion chamber and the secondary passageway,

said passage providing an outlet for the burning gas in the combustion chamber and at the same time restraining the freedom ci flow of the gas thereby to provide heat to dry the fuel in the combustion chamber, said secondary passageway including a horizontally extending part receiving burning gas from the, passage .and a vertically extending part opening at its upper end into the boiler containing chamber and means for supplying external air to the burning gas in the horizontally extending part of the secondary passageway, said secondary passageway and passage provided withmeans coacting to cause the burning gas to whirl as it passes through the constricted passage and along the secondaryl passageway past said last named air supplying means.

CARL G. BROWN. 

